The cathode current collector serves several functions in a cell. First, the cathode current collector conducts the flow of electrons between the cell active material and the cell terminals. Second, the cathode current collector supports the cathode material utilized in the cell. But cathode current collector materials must maintain chemical stability and mechanical integrity in corrosive electrolytes throughout cell life. The availability of materials capable of operating at elevated temperatures are limited. Accordingly, whenever operating conditions are such that passivity is compromised, corrosion occurs.
Titanium has proven corrosion resistant as a cathode current collector material. However, at elevated temperatures i.e. 72.degree. C. or higher, titanium and other alloys used for fabricating cathode current collectors are known to exhibit corrosion when exposed to aggressive cell environments.
Another material proposed for use as a cathode current collector in cells is ferritic stainless steel. Japanese patent publication No. 186467 discloses using a ferritic stainless steel containing about 18-20 percent by weight chromium, 1.8-2.5 percent by weight molybdenum and the sum of interstitial elements titanium and niobium limited to less than 0.45 percent by weight.
Furthermore, Japanese patent publication No. 15067 discloses using a ferritic stainless steel containing about 29-31 percent by weight chromium, 1.7-2.3 percent by weight molybdenum and the sum of interstitial elements carbon and nitrogen limited to less than 0.015 percent by weight.
Further, limitation of carbon and nitrogen to such low levels as disclosed in Japanese publication No. 15067 requires costly melting practices such as vacuum melting at the mill producing the high purity ferritic stainless steel.
Therefore, it would be highly desirable to provide an improved ferritic stainless steel cathode current collector material that does not require costly melting practices and provides a high corrosion resistance particularly where elevated temperature storage and performance is required thereby increasing cell longevity compared to cathode current collector materials such as titanium and to other ferritic stainless steels.